1. Field of the Invention
The present invention relates to an ink jet print head and a method of manufacturing thereof. More in particular, the present invention relates to method of manufacturing an ink jet print head having improved adhesion characteristics between its functional parts.
2. Description of Related Art
The present invention relates to an ink jet print head and in particular a print head of the type in which droplets of ink are expelled from a nozzle by rapid heating of a resistive element contained within an ink collecting chamber and disposed next to the nozzle.
The ink collecting chamber and the resistive element are formed within a multi-layer board realized on a silicon substrate using well known methods of construction of integrated circuits.
In short, various layers are deposited on a face of the wafer to make up the ejection resistors and the active electronic components. After that, a barrier layer of photopolymer is coated on the wafer. Using photolithographic techniques, the ejection chambers and the microidraulic conducts for the ink delivery are made in the photopolymer barrier layer and nozzle plates provided with ejection nozzles made in correspondence with the cells is mounted. A plurality of print heads, usually more than two hundreds, are made for each wafer.
A variety of different methods have been implemented in order to secure the nozzle plate to the barrier layer. These methods include but are not limited to the use of a separate layer between the orifice plate and barrier layer which contains one or more compositions that are designed to adhere these components together.
U.S. Pat. No. 5,278,584 discloses representative materials used for this purpose, which involves a number of chemical products, such as, for example uncured poly-isoprene photoresist which is applied using standard photolithographic techniques.
U.S. Pat. No. 5,198,834 describes the application of a photoresist composition sold under the name “Waycoat SC Resist 900” (Catalog No. 839167) by Olin Hunt Specialty Products, Inc. This composition is diluted with a product known as “Waycoat PF Developer” (Catalog No. 840017) and thereafter developed using “Waycoat Negative Resist Developer” (Catalog No. 837773), with both of these materials likewise being sold by Olin Hunt Specialty Products, Inc. as previously noted. Other materials which have been employed as adhesive compounds to attach the orifice plate to the barrier layer include but are not limited to polyacrylic acid, as well as acrylate and epoxy-based adhesives.
U.S. Pat. No. 6,155,676 discloses a printhead with improved durability characteristics comprising a substrate which includes an ink ejector system, a barrier layer, and an orifice plate having a bottom surface made of rhodium affixed to the barrier layer so that the rhodium-containing bottom surface is securely attached to the barrier layer. The use of rhodium in the bottom surface is described to provide improved adhesion characteristics without the use of separate adhesives.
U.S. Pat. Appl. Pub. 2003/0207209 discloses a method for making an ink jet printhead comprising applying a resin layer containing radiation curable resin formulation to a surface of a semiconductor chip containing resistive and conductive layers on the surface thereof, curing the resin layer by exposure to actinic radiation to provide a cured resin layer, aligning and attaching a nozzle plate to the semiconductor chip with an adhesive to provide a nozzle plate/chip assembly, and attaching a TAB circuit or flexible circuit to the nozzle plate/chip assembly. The resin layer provides the planarization of the surface of the chip prior to attaching the nozzle plate to the chip and at least two adhesive dots are provided on at least two diagonally opposed corners of the nozzle plate to hold the nozzle plate and the semiconductor chip in alignment.
U.S. Pat. No. 6,315,385 discloses a method for assembling a thermal ink jet printhead by applying an appropriate amount of adhesive to one or both of a nozzle plate and a barrier layer, wherein the orifice plate is provided with projections which matches with locators provided in the barrier layer to substantially hold the orifice plate and the printhead die in place to align each orifice with a corresponding transducer.
The proposed methods to secure the nozzle plate to the photopolymer barrier layer require a bonding process generally involving the application of a pressure at high temperature between the nozzle plate and the photopolymer barrier layer. Such a bonding process is generally referred as thermocompression bonding. Usually, the applied pressure ranges from 1 to 5 bar, and the temperature ranges from 150 to 200° C.